Abstract
Large quantities of impact-related microspherules have been found in fine-grained sediments retained within seven out of nine, radiocarbon-dated, Late Pleistocene mammoth (Mammuthus primigenius) and bison (Bison priscus) skull fragments. The well-preserved fossils were recovered from frozen “muck” deposits (organic-rich silt) exposed within the Fairbanks and Klondike mining districts of Alaska, USA, and the Yukon Territory, Canada. In addition, elevated platinum abundances were found in sediment analysed from three out of four fossil skulls. In view of this new evidence, the mucks and their well-preserved but highly disrupted and damaged vertebrate and botanical remains are reinterpreted in part as blast deposits that resulted from several episodes of airbursts and ground/ice impacts within the northern hemisphere during Late Pleistocene time (~46–11 ka B.P.). Such a scenario might be explained by encounters with cometary debris in Earth-crossing orbits (Taurid Complex) that was generated by fragmentation of a large short-period comet within the inner Solar System.
Highlights
During the time period leading up to the Last Glacial Maximum (~23–19 ka B.P.), when eustatic sea level was substantially lower, Alaska and the Yukon Territory were part of the largest circumarctic area to remain unglaciated, called Beringia (Fig. 1), which extended from eastern Siberia (Chukotka) across the exposed Bering Strait region into Alaska and western Canada[1,2]
The accelerator mass spectrometer (AMS) radiocarbon dates for the Beringian megafaunal skull fragments range between ~48 and 18 ka B.P. (Table S1) and are similar to those commonly determined for megafaunal bones and carcasses recovered from Alaskan and Yukon mucks[20,25,47] and Siberian Yedoma deposits[5,25,47]
Our results suggest that large amounts of melt-quenched impact spherules, associated with Pleistocene megafaunal remains, were deposited in the mucks of eastern Beringia after ~48 kyr
Summary
During the time period leading up to the Last Glacial Maximum (~23–19 ka B.P.), when eustatic sea level was substantially lower, Alaska and the Yukon Territory were part of the largest circumarctic area to remain unglaciated, called Beringia (Fig. 1), which extended from eastern Siberia (Chukotka) across the exposed Bering Strait region into Alaska and western Canada[1,2]. Expeditions to Alaska[12,13,14] and the Yukon Territory[14,15] found large quantities of megafaunal bones along beaches, riverbanks, and in minor-stream valleys[8]. The fossil bones collected included those of bison, mammoth, horse, musk ox, moose, lynx, lion, camel, mastodon, bear, and caribou, with many of these animals appearing as frozen partial carcasses or mummies[1,8,17]. Many tens of thousands of specimens were collected in the 20th century from Alaska and the Yukon Territory[5,8,19], and hundreds to thousands more are still being recovered every year from mines in the Klondike district alone[1]. Uniformitarian explanations can often appear inadequate, in providing a clear picture of how, for instance, animals found as frozen carcasses were quickly killed, often dismembered, and buried without normal predation, scavenging, or decomposition prior to freezing[5]
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